This project will try to characterize a new class of cells in lymphoid organs. The cells are called dendritic cells because they exhibit many cell processes or dendrites. Such cells have long been thought to exist in lymphoid organs and recently we have isolated a distinctive population of dendritic cells in vitro. We will try to learn more about the relation of these dendritic cells in vitro with those that have been described in situ. We will pursue the suggestive evidence that dendritic cells have an important function in two types of immune responses: the production of antibody secreting or plasma cells, and the development of germinal centers. The latter are collections of proliferating lymphocytes felt to be involved in the generation of immunologic memory. We will study these possible functions of dendritic cells in the intact animal and in two new tissue culture systems.